Thermal switch



Aug. 20, 1935. -rz 2,011,610

THERMAL SWITCH Filed Sept. 13, 1934 WITNESSES: INVENTOR Patented Aug.20, 1935 THERMAL SWITCH Edward Bletz, Lexington, Ohio, assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania Application September 13, 1934, Serial No.743,863 9 Claims. (Cl. zoo-122) My invention relates to temperaturecontrol devices, and particularly to thermally actuable switches.

An object of my invention is to provide a relatively simple, compact andinexpensive thermallyactuable snap-acting switch.

Another object of my invention is to provide a relatively -smallthermally-actuable switch that shall provide a. relatively largedistance between cooperating contact members when moved to openposition.

Another object of my invention is to provide a thermally-actuable switchassembly of the snap-acting type that shall provide electric means toreduce the temperature differential of operation of the switch, whichmeans is carried by and movable with the bi-metallic snap-actingelement.

Other objects of my invention will either be apparent from the followingdescription thereof,

or will be pointed out hereinafter.

In practicing my invention, I provide a base having mounted thereon aplurality of spaced contact members and terminals, and a snapactingbmetallic disc having two opposed limiting positions and operating fromone position to the other with a snap-action and having also arelatively large temperature differential of operation, which disc isadjustably supported on the base. The disc has mounted thereon andinsulated therefrom, a. corresponding plural ty of contact members whichare fixed or rigid relatively to the disc, together with an electricconnector extending between the contact members on the disc, whichconnector may be an electric resistor element. Means are furtherprovided to limit the upward dish of the disc, that is, to limit theamount of dishing of the disc when it is moved away from the base to itsopen position.

In the single sheet of drawings:

Figure l is a top plan view of one form of device embodying myinvention;

Fig. 2 is a view in lateral section therethrough taken on the line 11-11of Fig. 1;

Fig. 3 is a view in section through the structure shown particularly inFig. 2 of the drawing, and taken on the line III-m thereof;

F 4 is a similar view to that of Fig. 3 but taken on the line IV-IV ofFig.

Fig.5isatopplanview ofamodified form of device embodying my invention; I

Fig. 6 is a view in lateral section through such 'a device, taken on theline VL-VI of Fig. 5;

Fig.7isaviewinlateralsection throughthe device shown in Fig. 6, andtaken on the line VII-VII thereof; and,

Fig. 8 is a view in lateral section through the device of Fig. 6 andtaken on the line VIIIYHI thereof.

The device embodying my invention is shown in several of its preferredforms, and has reference more particularly to a, thermostatic snapactingswitch embodying a dished bimetallic disc of the type disclosed andclaimed in Patent No. 1,448,240 to J. A. Spencer. Briefly described, thebimetal disc is initially fiat and is then given a certain dishingwhereby the movement of one part of the disc relatively to a fixed partof the same disc is a discontinuous function of the change of ambienttemperature. That is, the disc will, in its normal operating conditions,occupy one of its two limiting positions until the ambient temperaturehas changed through a relatively very large value when the disc willsuddenly move with a snap-action to its other or opposite limitingposition.

In all of the structures which have thus far been utilized, the contactmembers mounted on and movable with the moving part of the disc haveincluded a loosely mounted contact-bridging member movablelongitudinally of its axis on a supporting stud in order that properoperative engagement might be effected between the contact bridgingmember and one or a plurality of fixed contact members mounted on thebase. This lost motion of the contact-bridging member insulatedlysupported by the disc made it necessary to insure that the disc wouldmove through a relatively large distance in order that the necessary gapor distance between the cooperating fixed and movable contact members inthe open position of the switch would be obtained. In contradistinctionto this, the contact members, both fixed and movable, in the deviceembodying my invention are rigidly or fixedly secured to theirrespective supports, thereby obtaining certain very desirable resultswhich will be set forth more clearly hereinafter.

Referring first to Figs. 1 to 4, inclusive, of the drawing, asnap-acting thermally actuable switch it includes a base it which ishere shown as of substantially circular outline and as made of metal.However, I do not wish to be limited to either the circular outline orcontour or to the use of metal. A semi-circular mica sheet I! is locatedagainst one face of base plate It and is held in proper operativeposition thereagainst by the body portions ll of two contact memberswhose contact-en aei a surfaces are preferably made flat and of theshape shown in Figs. 2 and 4 of the drawing where the same aredesignated by the numeral I9. I may make this engaging surface with arelatively thin layer 2| of a non-oxidizing material, such as silver.The body I! extends through a suitable opening in thebase I3, through asmall washer 23 of electric-insulating material, through an opening inone arm of a terminal member 25, which may be of substantially L-shape,and also through an opening in a metal washer 21 against which the outerend of a body I! may be hammered over to support all of these parts intheir proper operative positions substantially as shown in the drawing.It will be noted that I provide two such terminal members spaced apart asuitable distance, that is, these contact members are located adjacentto and within the periphery of the disc l3, both of these being locatedat one side of a diametral line.

A bimetallic disc 29 of the kind mentioned hereinbefore is locatedadjacent to one side of the base l3 or adjacent to the spaced contactmembers I! insulatedly supported on the base l3. The bimetal disc 29 isdished as shown, the initial amount of dishing being relatively large sothat the change of ambient temperature necessary to cause the disc tomove from one of its fixed positions to its other opposite position willbe very large.

An adjustable support for the central part of the disc 29 may comprise astud 3| having screw-threaded engagement with the base l3 substantiallycentrally thereof, two collars 33 and 35 being provided at one end ofthe stud 3| and on opposite sides of the centrally perforated disc 29 toloosely hold the same. Means for turning the stud 3| in order to adjustthe disc relatively to the contact members onthe base may include an arm3! which may be turned by an operator.

The disc 29 has two openings or perforations adjacent to but within theouter periphery of the disc and a plurality of contact members 39 arerigidly and insulatedly secured to the disc 29 by body portions of thecontact members extending through the opening in the disc and headed orriveted over on the opposite side thereof against metal washers ll in amanner well known 1 in the art. It will be noted that I thus provide twocontact members fixedly insulatedly mounted on and supported by the discand movable therewith, and since these two contact members are alsolocated at one side of a diametral line, I

1 provide a fixed abutment 43 for the opposite side of the disc, whichabutment is in the form of a small stud having a portion extendingthrough and riveted over against the base I3. I provide this abutmentfor the purpose of ensuring that the disc 29 'will be symmetricallystressed when the switch is in its closed position.

By suitable turning movement of the externally screw-threaded stud 3irelatively to the Epxening in base l3, it is possible to reduce the tialdish of disc 29 so that the temperature value at which it will operatefrom the position shown in Fig. 2 of the drawing, will be different.

from that at which the free and unconfined disc would operate. In otherwords, the temperature differential of operation of the disc has beenchanged by mechanical means. It is to be further noted that'while thetemperature differential of operation of the free disc may be on theorder of several hundred degrees Fahrenheft, it is usually desirable tohave a much smaller temperature differential of operation of the switchin actual operation in order to more closely regulate or control thetemperature of an electric device such as an electrically heated or anelectric heating appliance which my improved thermal switch is tocontrol.

Let it be assumed for illustrative purposes only, that the highexpansion component of bimetal disc 29 is on the underside of disc 29,so that an increase in the ambient temperature is necessary to cause theswitch, or more particularly the disc,

to operate to open a circuit. A movement of stud 3| to reduce the amountof dishing of the disc will, therefore, result in reducing the hightemperature value at which the disc will operate to open the circuitcontrolled thereby.

Means for raising the low temperature value at which the disc willoperate are provided in the shape of a plurality of stop pins 45 screwedinto the base l3 and extending through suitable openings 41 in the disc29, these stop pins being located adjacent to but inside the peripheryof the disc.

Another use of the arm 31 mounted on one end of stud 3| is that itpermits of manually varying the operating temperatures of the disc, thatis, it permits of varying the value of the ambient temperature at whichthe disc will move from one to the other of its opposing limitingpositions with a snap-action, while maintaining a substantially fixedtemperature differential of operation. Thus it is possible to so turnthe arm 31 that the disc 29 will move by thermal action to open positionat 600 F. and return to its closed position at 500 F., or to so adjustarm 31 by a turning movement thereof that disc 29 will open at 300 F.,and return at 200 F. It is to be understood, however, that these figuresare given for illustrative purposes only, and that they may vary withinwide ranges.

I provide an electric conductor 49 in the shape of a thin flat strip ofmetal extending between the two contact members 39 mounted on the disc29 but spaced from the inner side of disc 29. In other words, the pathof the current through device I I is from a conductor connected to oneof the terminals 25 into and through the body portion 11, into andthrough the head IS, the nonoxidizing layer 2|, into the cooperatingengaging contact member 39, which as may be noted, has a small areasurface thereof in engagement with the flat contact member on the base,into and through the conductor 49, from there into and through the othercontact member 39, through the non-oxidizable layer 2| on the othercontact member l9 and from there through the body portion I I and to theother or out-going terminal member 25.

Referring now to Figs. to 8 inclusive, of the drawing, I have thereillustrated a modified form of device embodying my invention which Ibelieve to be somewhat simpler and less expensive. The assembly 5|includes a base plate 53 which is shown as being made of metal but mayalso be made of a suitable electric-insulating material. The base plate53 is provided with two diametrally located openings 55 therein near theperiphery of the base through which. extend the body portions 5] of thetwo fixed. contact mem bers 59 which are also preferably made with aflat outer surface and which may be provided in the manner well known inthe art with a thin layer SI of a non-oxidizing metal. Small plates orwashers B3 of electric insulating material, such as mica, are located ateach side of. the plate 53 around the openings 55 in order to properlyinsulate the current-conducting portions from the base 58 when the sameis made of metal. A terminal member 65, here shown as of substantiallyL-shape, is associated with the body portion 51, thin layers 61 of metalbeing provided to permit of riveting over the outer end of body portion51 against the outer washer 81 to hold the assembly in fixed position onthe base 53. A snap-acting bimetal disc 69 of the same type as washereinbefore described for disc 29 is adjustably mounted on andsupported from the base 53 as by an externally screw-threaded stud 1ihaving a manually actuable arm 18 thereon to efiect turning movement ofthe stud H relative to the base. It is to be noted that the stud llextends through the base plate 58 centrally thereof and is provided withsuitable flanges l5 and 11 to loosely hold and support the disc 89 onthe stud I l.

A pair of contact members I8 having rounded engaging surfaces and bodyportions 8i of reduced diameter are insulatedly mounted on and supportedby the disc 89 near the periphery thereof as by the use of small washers83 of electric insulating material all in the manner known in the art.

Means for electrically connecting the two contact members 19 includes astrip 85- of electric conducting material, the ends of which are locatedunder the heads of contact members I8, the strip 85 extendingdiametrally of the disc 68, and being provided with an opening 81therein surrounding the stud 1| with sufllcient clearance. A pair ofstop pins 88 are provided which are substantially the same as the stoppins 45 hereinbefore described. They alternate with the contacts 59 asto their peripheral position.

It will be noted that the device embodying my invention provides contactmembers fixedly mounted on the disc 89 but electrically insulatedtherefrom, the construction being such that there are no loose parts ofthe contact members on the disc, that is, all parts of the contactstructure supported on the disc and movable therewith occupy fixedpositions relatively to the disc. It is, therefore, evident that whenthe snap-acting bimetallic disc is operated, it will move the contactmembers secured thereto through a distance which is substantially thesame as that through which the disc itself moves, so that it is possibleto reduce the distance through which the movable part of the disc needsto move to obtain a certain length of gap between the cooperating andinitially fixed and movable contact members.

I have already hereinbefore set forth how, by mechanical means, thetemperature differential of operation of the disc itself is varied, asby reducing the maximum temperatureat which the disc will operate and byincreasing the minimum temperature at which the disc will operate.Another important element of my invention consists in the provision ofmeans by which the values of the ambient temperature at which the discwill operate can be varied and this means comprises making the connector48 or the connector 85 of a resistor material whereby when the same areindividually traversed by the circuit current, a small amount of heatwill be generated which will affect the disc. In other words, by makingthe conductor 48 or 85 of a resistor material a small auxiliary heateris provided located inside of the disc and movable therewith to add asmall amount of heat to that imparted to the disc by the ambienttemperature. It is to be noted, of course, that this resistor conductor(or auxiliary heater) is properly operative only during the time thatthe circuit is closed, and that it is inoperative to generate heat andimpart the same to the disc while the circuit is open as bydisengagement of the cooperating fixed and movable contact members.

For illustrative purposes, let it be assumed that the bimetal disc 28(or 68) is so adjusted that it will move from its closed-circuitposition to its open-circuit position when the ambient temperature hasreached a value of say 300 F. If now, the resistor conductor 49 (or 85)is such as to cause a temperature rise of 25, it is evident that theambient temperature need rise only to a value of 275 F. before the discmoves with a snap-action from its closed circuit to its open circuitposition.

In structures of this general kind where the contact member supported bythe disc had a loosely mounted part it was highly undesirable to operatethe device with the base plate lowermost, since any lost motion resultedin the movable part of the contact member on the disc not moving as faraway from the fixed contact member as did corresponding portions of thedisc. No such trouble occurs in a device embodying my invention and itis, therefore, immaterial as to whether the disc is mounted above thebase or vice versa.

The use of the resistor conductor located closely adjacent to andmovable with the movable part of the disc provides a very simple andemcient means for still further reducing the amount of variation in theambient temperature which it is necessary to effect to cause operationof the disc and still obtain a sufliciently large gap betweencooperating contact members.

The device embodying my invention thus provides a compact, simple, andhighly efficient snap-acting thermostatic switch effective for theintended purpose of controlling, with little or no arcing, a circuitcarrying a current of relativeLv high value and of relatively highvoltage.

Various modifications may be made in the device embodying my inventionwithout departing from the spirit and scope thereof, and I desire,therefore, that only such limitations shall be placed thereon as areimposed by the prior art or are set forth in the appended claims.

I claim as my invention:

1. A quick-acting thermal switch including a base, a. plurality of fixedcontact members thereon, a snap-acting bimetal disc adjacent to andsupported from the base, a corresponding plurality of spaced contactmembers fixedly and insulatedly mounted on the disc, and an electricconductor electrically connecting the contact members on the disc andmovable therewith.

2. A quick-acting thermal switch including a base, a plurality of flatcontact members fixedly mounted on the base, a snap-acting bimetal discadjacent to and supported from the base, a corresponding plurality ofspaced contact members fixedly and insulatedly mounted on the disc andhaving rounded contact surfaces, and an electric conductor connected toand extending between the contact members on the disc and locatedbetween the disc and the base.

3. A quick-acting thermal switch adapted to be operated by variations inthe ambient temperature including a base, a plurality of spaced contactmembers on the base, a snap-acting bimetal disc adjacent to andsupported by the disc, said disc having predetermined upper and loweroperating temperature values, contact members on the disc cooperatingwith the con- 5 tact members on the base, and electric means connectingthe contact members on the disc and movable therewith for varying one ofsaid ambient temperature values at which the disc operates.

4. A quick-acting thermal switch adapted to be operated by variations inambient temperature, including a base, a plurality of contact members onthe base, a snap-acting bimetallic disc'adjacent to and supported by thedisc, said disc having a predetermined temperature differential ofoperation, contact members on the disc, and electric means connectingthe contact members on the disc and movable therewith for reducing thevariation in the ambient temperature necessary to cause the disc tooperate from one to the other of its positions.

5. A quick-acting thermal switch adapted to be operated by variations inambient temperature, including a base, a plurality of contact members onthe base, a snap-acting bimetallic disc adjacent to and supported by thedisc, said disc having a predetermined temperature differential ofoperation, contact members on the disc, and electric means movable withthe disc and controlled by the cooperating contact members, for reducingthe amount of the change in ambient temperature necessary to causeoperation of the disc from one position to another position.

6. In a quick-acting thermal switch responsive to variations in ambienttemperature, the combination with a base, a plurality of contact memberson the base, a snap-acting bimetallic disc adjacent to the base,cooperating contact members on the disc, adjustable means supporting thedisc from the base, said disc-supporting means effecting a variation oi.an ambient temperature value at which the disc operates, by adjustmentthereof relatively to the base, of a current-traversed member supportedby the disc and movable therewith for independently eflecting avariation of an ambient temperature value at which operation of the discis eiIected.

7. In a quick-acting thermal switch, the combination with a base, aplurality of spaced contact members on the base, a snap-actingbimetallic disc adjacent to the contact members, and having a relativelylarge temperature diI- ferential of operation, cooperating contactmembers rigidly insulatedly mounted on the disc, means supporting thedisc from the base and adjustable relatively thereto to vary one 0! theoperating temperature values or the switch, and means on the base andcooperating with the disc to vary the other operating temperature valueof the switch, of electric means supported by and movable with the discfor additionally varying the first-mentioned operating temperature valueof the switch.

8. In aquick-acting thermal switch, the combination with a base, aplurality of spaced con tact members on the base, a snap-actingbimetallic disc adjacent to the contact members and having initially arelatively large temperature differential of operation between its offand on positions, cooperating contact members rigidly and insulatedlymounted on the disc, means supporting the disc from the base andadjustable relatively to the base to vary one of the operatingtemperature values of the switch to reduce the initial diil'erential,and means on the base cooperating with the disc to vary the otheroperating temperature value to reduce the initial differential, of anauxiliary heater electrically connecting the contact members on thedisc, movable therewith and effective to independently vary thefirst-named operating temperature value to additionally reduce thetemperature difl'erential of operation.

9. In a quick-acting thermal switch operative in response to variationsin ambient temperature, the combination with a base, a plurality ofspaced contact members on the base, a snap-acting bimetallic discadjacent the contact members on the base and having initially arelatively large difference between the high temperature at which itsnaps to open position and the low tempera ture at which it snaps toclosed position, co-

operating contact members rigidly and insulat edly mounted on the disc,means supporting the ,disc from the base and adjustable relativelythereto to lower the high ambient temperature value at which the discsnaps to open position, and mechanical means on the base and cooperatingwith the disc to raise the low ambient temperature value at which thedisc snaps to closed 1;

position, of an auxiliary heater connecting the the current traversingthe switch to additionally lower the high ambient temperature value atwhich the disc snaps to open position.

EDWARD BLETZ.

lol

i contact members on the disc and traversed by

